1. Field of the Invention
The present invention relates to an image reading apparatus for optically reading an image on an original document.
2. Background Art
With the recent development of the computer technologies, the network technologies, etc., image processing systems are now used widely that are equipped with an image reading apparatus such as a scanner, a host computer (hereinafter referred to simply as “host PC”) such as a personal computer, and an image output apparatus such as a printer. Such image processing systems are usually configured in such a manner that when the image reading apparatus has read a color image on an original document as RGB multi-valued data, the RGB multi-valued data are transferred to and stored in the host PC and then the image output apparatus receives the RGB multi-valued data and prints those data by performing color conversion processing into the YMCK color space, screen processing, etc. Among such image processing systems are ones capable of printing RGB multi-valued image data without depending on the kind of image processing function of the image output apparatus because the host PC performs image processing that should inherently be performed by the image output apparatus (e.g., JP-A-11-98353). There also exist image processing systems in which RGB multi-valued image data obtained by the image reading apparatus can be output by the image output apparatus without intervention of the host PC (e.g., JP-A-2002-314736).
Incidentally, in each of the above conventional configurations, the image processing necessary for printing RGB multi-valued image data such as color conversion processing, gradation correction processing, and screen processing depends on the image processing function of the image output apparatus or the image processing function the host PC takes over. Further, RGB multi-valued data that are read by the image reading apparatus are not necessarily intended for printing. Therefore, depending on the kind of image processing function of the image output apparatus (i.e., the type of image output apparatus) or the kind of image processing function the host PC takes over (i.e., the kind of software that runs on the host PC), scanned-in RGB multi-valued image data may be printed without being subjected to proper image processing. This may cause image quality problems; for example, characters are blurred and the background is fogged in the case of a text original document or the like and moiré occurs in the case of a photograph original document consisting of halftone dots or the like. Further, since RGB multi-valued image data are sent to the host PC or the image output apparatus, the transfer load and the image processing load in each apparatus are increased, which results in a problem of reduction in productivity.